In recent years, connector technology has not kept pace with the solid state circuit technologies. As the solid state chips have become capable of supporting more and more complicated circuit patterns, the input-output densities, (i.e., the fine signal wires that are necessary to communicate one circuit chip to another usually given in the number of input-output circuits per cubic inch) are also increasing exponentially. As the density of input-output circuits increases, the maintenance and parts damage percentage have gone up and connectors have now become one of the least reliable components within electronic subsystems. For example, the interconnection from chip to chip carrier is accomplished using a 0.002 inch diameter wire and are more reliable than typical connector pins.
To put the problem in perspective; during the vacuum tube era, where considerable power was required for the vacuum tubes, it was common practice to have the complete circuit subassembly serviced by a large cable with a relatively large connector with 1/16-inch diameter pins having to be mated. With the advent of circuit compression through solid state electronics these requirements have now arisen to a point where it is not uncommon for a connector to be required to make 200 to 400 contacts, where the contacts are only 0.030 inch in diameter. With this high density of small pins it is very easy to have one or more of the pins become deflected and/or mate improperly causing poor contact or making the connector unusable. This is why connector failures have become one of the dominate failure modes in avionics equipment.
The principal way of avoiding these pin chrunching connector mating operations is to use what is commonly called a zero insertion force (ZIF) connector. In this type of connector the pins and sockets are mated without any contact of the mating surfaces themselves so that there is very little mating force. With the two halves mated, a latch or cam mechanism is operated to engage all of the contacts and complete the circuit. These ZIF connectors have become very popular and sometimes very exotic.
The one major drawback with prior art designs is that since the connector is usually in the bottom of the housing into which the circuit boards are to be mated, it is very difficult to get to the connector to perform the latching operation.
Front panel operated ZIF connectors have eliminated this problem because the board or module can be inserted from the end of the connector rather than normal to it. This permits the end of the connector to be accessible from the open side of the electronics housing such that when the card or module is mated with the connector it is easy to reach the handle and operate the mating mechanism. Card edge front panel operated ZIF connectors are commercially available at this time, but their size and fabrication technique have not permitted a very high density of connections and they require a very large space for obtaining proper positioning and operation.
A second problem associated with the ZIF connector has to do with the very fine film that develops on contact surfaces from contamination, such as dirt, smoke, etc., which must be wiped off. On any connector it is necessary to have a finite wiping action so that the film is broken and metal surfaces are in intimate contact.
In the high density electronics that have been previously referred to, the design of the backplane or mother board becomes important. As the solid state devices used on the circuit boards have become more complicated and carry many more functions, they also have a large number of connections. This means that relatively small boards now may have as many as four hundred contacts per board that must be mated with the mother board. This high density of traces or terminals have required the use of multi-layer mother boards.
In some applications, particularly for military use, the mother boards have exceeded fifteen layers. The typical connectors used for mating of the subboards perforate the mother board like a picket fence. These piercing type connector terminals require a hole through all layers of the multilayer mother board and each of these holes must be plated through, which requires very stringent quality controls.
Examples of this type of connector are disclosed in the following patents: U.S. Pat. No. 4,196,955, "Zero Insertion Force Connector," by John W. Anhalt; U.S. Pat. No. 3,793,609, "Low Insertion Force Printed Board Connector," by William McIver; U.S. Pat. No. 4,303,294, "Compound Spring Contact," by Wilbur A. Hamshere, Jr., et al; U.S. Pat. No. 4,261,631, "Connector for Printed Circuit Board," by Bernard Guilcher, et al; U.S. Pat. No. 3,977,747, "Zero Insertion Force Connector," by Kamal Shawiky Broutros; and U.S. Pat. No. 3,665,370, "Zero-Insertion Force Connector," by Karl Wilhelm Hartmann. Note that in all of these patents the mother board terminals also act as the locking means for the circuit board and the mother board is pierced by the terminals.
Prior attempts to provide Zero-Insertion Force Connectors which do not pierce the mother board can be found in Applicant A. Morrison's pending application, Ser. No. 521,802 "Front Panel Operated-Zero Insertion Force Housing For Circuit Boards and an Electrical Connector Therefor".
Therefore, it is a primary object of this invention to provide a housing for connecting circuit boards to a mother board wherein the circuit board can be installed with zero insertion force.
It is another object of this invention to increase the allowable electrical terminal contact density for a housing adapted to connect circuit boards with a mother board.
Another object of this invention is to provide a housing for connecting circuit boards to a mother board with zero insertion force and providing front panel locking of the circuit boards therein.
A further object of this invention is to provide a housing for connecting circuit boards to a mother board wherein the mother board is not pierced by electrical terminals; i.e., surface mounted.
A still further object of this subject invention is to provide a housing for connecting circuit boards to a mother board wherein the electrical connector wipes and cleans off the electrical terminals on the mother board, ensuring good electrical contact upon the connection to the mother board terminals.